Abstract : Tokamaks are devices aimed at studying magnetic fusion. They operate with high temperature plasmas containing hydrogen, deuterium or tritium. One of the major issue is to control the plasma-wall interaction. The plasma facing components are most often in carbon. The major drawback of carbon is the existence of carbon deposits and dust, due to erosion. Dust is potentially reactive in case of an accidental opening of the device. These deposits also contain H, D or T and induce major safety problems when tritium is used, wich will be the case in ITER. Therefore, the understanding of the deposit formation and structure has become a main issue for fusion researches. To clarify the role of the deposits in the retention phenomenom, we have done different complementary characterizations for deposits collected on similar places neutralizers in tokamaks Tore Supra France and TEXTOR Germany. Accessible microporous volume and pore size distribution of deposits has been determined with the analysis of nitrogen and methane adsorption isotherms using the BET, Dubinin-Radushkevich and $\alpha$s méthods and the Density Functionnal Theory DFT. To understand growth mechanisms, we have studied the deposit structure and morphology. We have shown using Transmission Electron Microscopy TEM and Raman microspectrometry that these deposists are non amorphous and disordered. We have also shown the presence of nanoparticles diameter between 4 and 70 nm which are similar to carbon blacks : nanoparticle growth occurs in homogeneous phase in the edge plasma. We have emphasised a dual growth process: a homogenous and a heterogeneous one.